DESCRIPTION (provided by the investigator): The long-term goal of this research is to understand the viral and host determinants that allow for efficient infection of the human respiratory tract by influenza viruses. Influenza virus is a major respiratory pathogen affecting people of all ages and a perpetually re-emerging public health threat causing both annual epidemics and sporadic pandemics in the human population. Despite the prevalence of influenza, little is known about how this virus interacts with its target tissue for infection, the human ciliated airway epithelium. Human influenza viruses bind to glycoconjugates containing terminal a2,6-linked sialic acids on target ciliated and non- ciliated cells in the airway epithelium to facilitate infection, yet the relevant underlying molecules in the airway that present these sialic acids have not been defined. Our preliminary data indicate that human influenza viruses interact with sialic acid on MUC1, a mucin protein that is tethered to the apical surface of airway epithelial cells and abundant throughout the respiratory tract. Mucin glycoproteins are a major constituent of mucus and are critical for normal lung function, as well as lung defense by trapping particulate matter and pathogens for removal from the airway. The consequences of MUC1 interaction with influenza virus with respect to the pathogenesis of this virus are currently unknown. We hypothesize that influenza virus interactions with MUC1 on the human airway surface impacts the ability of influenza virus to infect target epithelial cells. MUC1 may be facilitative for infection (i.e., act as a receptor molecule), or restrictive (i.e., act as a physically block). MUC1 may also initiate signal transduction pathways leading to anti-viral or pro-inflammatory cytokine responses that may influence the ability of influenza virus to replicate and spread. We propose to determine the role of MUC1 in influenza virus infection using both in vitro and in vivo model systems. Specific Aim 1 will characterize influenza virus binding, entry, replication and spread as well as the host cytokine response in both cell lines stably expressing human MUC1 and models of differentiated pseudo- stratified airway epithelium in which MUC1 expression is reduced or absent. Because the role of MUC1 in influenza virus infection is likely multi-factoral, Specific Aim 2 will investigate correlates of infection and host response in wild type mice compared to mice genetically deleted for Muc1 (the mouse homolog) to determine the overall contribution of this mucin to influenza virus pathogenesis. This research will provide a comprehensive analysis of a major mucin protein of the human respiratory tract in influenza virus infection and provides the basis for future studies investigating influenza virus infection in models, such as chronic lung disease models, where mucin expression is altered. [unreadable] [unreadable] [unreadable] [unreadable]